JAMB Biology 2021 Past Questions & Answers

Xylem is a complex plant tissue with two primary functions: transporting water and dissolved minerals from the roots to the rest of the plant, and providing mechanical support. The lignified cell walls of xylem vessels are strong and rigid, which helps to strengthen the stem and other plant parts, enabling the plant to stand upright.

Common mistake: Many students might confuse the function of xylem with that of phloem, incorrectly choosing 'conducting manufactured food' (D), or focus only on water transport and overlook its crucial supportive role.

Wind-pollinated flowers are adapted to release and capture pollen carried by wind. Their pollen grains are typically small, light, and smooth to be easily dispersed by air currents. Rough or spiny surfaces are characteristic of insect-pollinated pollen, as these features help the pollen stick to the bodies of insects. Therefore, rough spiny pollen is not a characteristic of wind-pollinated flowers.

Common mistake: Students often confuse the characteristics of wind-pollinated and insect-pollinated flowers, or they might overlook the 'not characteristic' part of the question and choose an option that is actually true for wind-pollinated flowers.

The question describes an animal with scales, teeth, nares (nostrils), and a backbone. The presence of scales and teeth together is a defining characteristic of reptiles. Among the given options, a lizard is a reptile that possesses all these features, while toads are amphibians, birds have feathers, and rats are mammals with fur.

Common mistake: Students might incorrectly choose 'toad' if they confuse amphibians with reptiles, or 'rat' if they overlook the 'scales' feature, as both have teeth and a backbone.

A food chain shows how energy flows from one living organism to another. It always starts with a producer, like grass, which makes its own food. The grasshopper eats the grass, the toad eats the grasshopper, the snake eats the toad, and finally, the hawk eats the snake. This sequence correctly represents the transfer of energy.

Common mistake: Students often get confused about the feeding relationships between animals, leading them to incorrectly place predators before their prey or misidentify what an animal eats, as seen in options A, C, and D.

The animal kingdom is broadly divided into two main groups based on the presence or absence of a backbone. Vertebrates are animals that have a backbone or vertebral column, while invertebrates are animals that do not have one. Flatworms and roundworms lack a backbone, which is the defining characteristic that places them in the invertebrate group.

Common mistake: Students might mistakenly choose option A because many invertebrates are small, but size is not the scientific basis for this classification, as some invertebrates like the giant squid are very large.

This question describes the process of osmosis. The salt solution is more concentrated (hypertonic) than the sap inside the Spirogyra cell, meaning it has a lower water concentration. Water always moves from a region of higher water concentration (inside the cell) to a region of lower water concentration (outside the cell), causing the cell to lose water and shrivel in a process called plasmolysis.

Common mistake: Students often mistakenly choose option B, confusing the hypertonic solution with a hypotonic one (like pure water), which would cause the cell to take in water.

A pollutant is a substance that harms the environment. Smoke, noise, and sulphur dioxide are all known to be harmful pollutants. Nitrogen gas, however, is the most abundant gas in our atmosphere (about 78%) and is essential for life, so it is not considered a pollutant in its natural form.

Common mistake: Students may get confused because they have learned that some nitrogen *compounds* (like nitrogen oxides from car exhaust) are pollutants, but the question refers to nitrogen gas, which is harmless.

To find the percentage water content, first calculate the amount of water absorbed by the soil: 50ml (initial) - 35ml (drained) = 15ml. Then, divide the absorbed water by the initial volume of water poured and multiply by 100 to get the percentage: (15ml / 50ml) * 100% = 30%. This calculation shows the soil retained 30% of the water.

Common mistake: Students often make calculation errors or incorrectly use the drained water volume as the denominator when calculating the percentage, leading to a wrong answer.

In a termite colony, which is a social insect group, there is a division of labour. When the primary king and queen die, the colony ensures its survival by nurturing some of the young termites, called nymphs, to become 'secondary reproductives'. These new reproductives then take over the role of laying eggs and fertilizing them, allowing the colony to continue.

Common mistake: Students often confuse the social system of termites with that of bees, mistakenly thinking workers can be specially fed to become reproductives, but in termites, the worker caste is sterile.

This experiment, known as a water culture or hydroponics, is used to study the minerals plants need. The culture solution contains water and dissolved minerals, which is a perfect environment for tiny green organisms called algae to grow, especially when exposed to light. If algae grow, they will compete with the plant for the minerals, which will spoil the experiment. Therefore, the bottle is darkened to block sunlight, preventing the algae from performing photosynthesis and growing.

Common mistake: Students might mistakenly choose option B, thinking that darkness is a direct requirement for root growth like soil is, but the main scientific reason in this specific experiment is to prevent the growth of competing algae.

In the mammalian respiratory system, the actual exchange of gases occurs in the alveoli. These are millions of tiny, balloon-like air sacs at the end of the bronchioles. Their very thin walls and rich blood supply allow oxygen to easily diffuse into the blood and carbon dioxide to diffuse out.

Common mistake: Students often mistakenly choose 'lungs' because gas exchange does happen within the lungs, but the question asks for the specific structure where the exchange takes place, which is the alveoli.

Aged red blood cells, also known as erythrocytes, are primarily destroyed in the liver and spleen. The liver contains specialized macrophages called Kupffer cells that engulf and break down these old cells. This process is crucial for recycling components like iron and maintaining healthy blood, which is the medium of the transport system.

Common mistake: Students might incorrectly choose the kidney (D) because it is involved in filtering blood, but its main role is waste excretion, not the destruction of aged red blood cells.

The villi are tiny, finger-like projections found in the inner lining of the small intestine. Their numerous folds and projections significantly increase the internal surface area of the small intestine. This large surface area is crucial for efficient absorption of digested food nutrients, such as glucose, amino acids, and fatty acids, into the bloodstream.

Common mistake: Students often confuse the roles of digestion and absorption, leading them to incorrectly choose option B, thinking villi increase surface area for digestion rather than absorption.

Benedict's solution is the chemical reagent used to test for the presence of reducing sugars. When a substance containing a reducing sugar is warmed with Benedict's solution, the colour changes from blue to green, yellow, orange, and finally forms a brick-red precipitate. Glucose is a simple reducing sugar, so it gives this positive result.

Common mistake: Students often confuse the test for reducing sugars with the test for starch, incorrectly selecting Starch (B), which is a non-reducing sugar and is tested for using iodine solution.

After food is digested and absorbed in the alimentary canal, the nutrient-rich blood must be processed by the liver. The hepatic portal vein is the unique blood vessel that carries this blood directly from the intestines to the liver. This allows the liver to filter and process the absorbed nutrients before they are circulated to the rest of the body.

Common mistake: Students often mistakenly choose the hepatic vein because it is also connected to the liver, but it carries processed blood *away* from the liver to the heart, not *to* it from the alimentary canal.

Conjugation is a form of sexual reproduction in Paramecium where genetic material is exchanged. During this process, the diploid micronucleus in each partner undergoes meiosis, which involves two successive divisions to produce four haploid micronuclei. Therefore, the statement that each micronucleus divides twice is correct.

Common mistake: Students often mistakenly choose option C, confusing the roles of the two nuclei; it is the micronucleus that divides for reproduction, while the macronucleus actually disintegrates during conjugation.

Petrol often contains lead compounds, which are added to improve engine performance. When a person sucks petrol, this lead is absorbed from the mouth and gut into the bloodstream. This is very dangerous because lead is a toxic heavy metal that can build up in the body and cause serious health problems, including damage to the brain and nervous system.

Common mistake: Students might mistakenly choose iron because it is a well-known component of blood, but they forget that the question is about a harmful substance from petrol, not a normal blood component.

Bilharzia, also known as schistosomiasis, is a disease caused by parasitic worms whose life cycle involves freshwater snails as intermediate hosts. Applying molluscicides in water bodies kills these snails, thereby breaking the parasite's life cycle and preventing the spread of the disease. This is a direct and effective control measure against bilharzia.

Common mistake: Students might mistakenly choose option C (screening windows and doors with mosquito nets) because they associate disease control with common vectors like mosquitoes, overlooking the specific vector for bilharzia.

The human skeleton is divided into two main parts: the axial skeleton and the appendicular skeleton. The appendicular skeleton consists of the bones of the limbs (fore and hind limbs) and the girdles that attach them to the axial skeleton. These girdles are the pectoral girdle (shoulder) and the pelvic girdle (hip). Therefore, option A correctly lists all components.

Common mistake: Students often confuse the axial and appendicular skeletons, leading them to incorrectly include parts of the vertebral column like lumbar vertebrae (options C and D) which belong to the axial skeleton.

Aerenchyma tissues are specialized air-filled tissues found in aquatic plants like water lilies. These large air spaces provide buoyancy, enabling the plant to float on the water surface. This is a crucial adaptation for survival in aquatic environments, helping the plant access sunlight and exchange gases effectively.

Common mistake: Students might incorrectly choose 'dissected leaves' (B) as an adaptation for aquatic plants, but while they help reduce water resistance, they are not primarily for buoyancy.

The perception of smell in mammals starts when dissolved chemicals (odorants) in the air stimulate specialized sensory cells in the nasal cavity. These sensory cells then generate electrical signals. These signals are transmitted along the olfactory nerve, which carries the information directly to the brain for interpretation as a specific smell.

Common mistake: Students might choose options like A or C because they mention chemicals and nerve endings, but they often miss the critical detail that chemicals must be dissolved and that specific sensory cells are stimulated before the signal reaches the olfactory nerve and then the brain.

Over-crowding happens when a population grows very quickly. This occurs when the number of individuals being added is much higher than the number being removed. Statement I (High birth rate and high immigration rate) describes a high rate of addition to the population, while Statement III (Low mortality rate and low emigration rate) describes a low rate of removal. Combining these two factors leads to the fastest possible population growth and therefore, rapid over-crowding.

Common mistake: Students may mistakenly choose option C because it includes a high birth rate, but they fail to see that a high mortality and emigration rate would counteract this growth, preventing rapid overcrowding.

To find the percentage of occurrence, you first need to calculate the total number of all plants in the garden. This is 15 (Guinea grass) + 5 (Ipomoea) + 7 (Sida) + 23 (Imperata), which equals 50. Then, you divide the number of Imperata spp (23) by the total number of plants (50) and multiply by 100 to get the percentage. So, $(23 / 50)$ x 100 gives you 46%.

Common mistake: Students often mistakenly choose option D, confusing the direct count of Imperata spp (23) with its percentage occurrence.

Marine fish are adapted to live in salty water, meaning their body fluids have a higher salt concentration than freshwater. When placed in freshwater, which is hypotonic (less concentrated) compared to the fish's cells, water moves by osmosis from the freshwater into the fish's cells. This continuous influx of water causes the cells to swell and eventually burst, leading to the death of the fish.

Common mistake: Students might choose option C, thinking the cells would shrink, but this would only happen if the fish was placed in water saltier than its body fluids (hypertonic solution).

In a DNA molecule, the nitrogenous bases have specific partners: Adenine (A) always pairs with Thymine (T), and Cytosine (C) always pairs with Guanine (G). For the given DNA strand with the sequence TCA, we find its complementary strand by pairing each base. T pairs with A, C pairs with G, and A pairs with T. Therefore, the complementary base sequence is AGT.

Common mistake: Students might correctly determine the complementary bases are A, G, and T but then choose option A (ATG) by mixing up the correct order of the sequence.